Current analyzers, as are used as a matter of routine in analytics, forensics, microbiology and clinical diagnostics, are able to carry out a multiplicity of detection reactions and analyses with a multiplicity of samples. In order to be able to carry out a multiplicity of examinations in an automated manner, various automatically operating apparatuses for the spatial transfer of measuring cells, reaction containers and reagent liquid containers are required, such as, e.g., transfer arms with a gripper function, transport belts or rotatable transport wheels, and apparatuses for transferring liquids, such as, e.g., pipetting apparatuses. The machines comprise a central control unit which, by means of appropriate software, is able to largely independently plan and work through the work steps for the desired analyses.
Many of the analysis methods used in such analyzers operating in an automated manner are based on optical methods. Measurement systems based on photometric (e.g., turbidimetric, nephelometric, fluorometric or luminometric) or radiometric measurement principles are particularly widespread. These methods enable the qualitative and quantitative detection of analytes in liquid samples without having to provide additional separation steps. The determination of clinically relevant parameters, such as, e.g., the concentration or the activity of an analyte, is often implemented by virtue of an aliquot of a bodily fluid of a patient being mixed simultaneously or in succession with one or more reagent liquids in a reaction vessel, as a result of which a biochemical reaction is put into motion, which brings about a measurable change in an optical property of the test preparation.
The measurement result is, in turn, forwarded into a memory unit by the measurement system and evaluated. Subsequently, the analyzer supplies a user with sample-specific measurement values by way of an output medium, such as, e.g., a monitor, a printer or a network connection.
For the spatial transfer of liquid containers, provision is often made of grippers for gripping, holding and releasing a liquid container, said grippers being connected by way of a flexible connecting element to a horizontally and vertically movable transfer arm. EP-A2-2308588 describes an apparatus for transferring a liquid container, in particular for transferring tube-shaped reaction vessels (cuvettes), within an automated analyzer. The apparatus comprises a passive, elastically deformable gripper for a force-fit capture and hold of a liquid container and is suitable for receiving an individual cuvette placed in a receiving position, transporting said cuvette to a target position and putting it down there in a further receiving position.
Furthermore, it is often necessary for liquids contained in liquid containers to be mixed. To achieve precise measurement results, it is for example necessary for reaction mixes, that is to say, mixtures of a sample liquid to be analyzed, such as, for example, blood, plasma, serum, urine etc., with one or more reagent liquids, such as, for example, antibody solutions or the like, to be mixed uniformly. It may likewise be necessary for reagent liquids which contain sedimentable contents, such as, for example, particulate solid phases, such as, for example, antibody-coated latex particles, to be mixed prior to use in order that a homogeneous solution is formed.
For this purpose, FIG. 1 of EP-A2-2308588 describes a shaking device having a coupling pin which is movable about a vertical axis of rotation. For the mixing of a liquid sample in a liquid container, a method comprising the following steps is described:
a. receiving the liquid container by way of a gripper which is fastened by way of a flexible connecting element to an automatically movable transfer arm, wherein the gripper has a coupling hole; then
b. displacing the gripper with the liquid container to the shaking device; then
c. producing a connection between the gripper and the shaking device, wherein the connection is realized by insertion of the coupling pin of the shaking device into the coupling hole, which is provided on the gripper, in a direction coaxial with respect to the axis of rotation of the coupling pin; and then
d. moving the coupling pin.
The coupling pin moves eccentrically on a circular path and forces the decoupled gripper, and thus the liquid container and the liquid contained therein, to perform said circular movement, whereby mixing of the contained liquid is effected.
Theoretically, the gripper moves synchronously with the rotating coupling pin. In practice, it has however been observed that the contact or the coupling between coupling pin of the shaking device and coupling hole of the gripper is possibly at least briefly eliminated owing to the contact pin losing contact with the inner wall of the coupling hole. When the contact is subsequently restored, brief shocks can occur, which can likewise have an adverse effect on the mixing process.
Specifically, the opening of the coupling hole is normally slightly larger than the head end, which engages into it, of the coupling pin, in order that, during the coupling-in process, highly precise positioning of the coupling hole over the coupling pin, which would significantly slow the entire mixing process, can be dispensed with. Narrower manufacturing tolerances with regard to the coupling mechanism composed of the coupling pin and coupling hole would result in increased abrasion and wear, as a result of which more frequent exchange of the parts involved would be necessary, which in turn would result in increased maintenance outlay for the automated analyzer.
Owing to the brief elimination of contact between the coupling pin and coupling hole, a situation may arise in which a liquid sample is not mixed as desired, and as a result, an erroneous measurement result is generated.
The problem on which the present invention is based thus consists in improving the automated method, described in the introduction, for mixing a liquid sample in a liquid container such that the mixing process takes place uniformly, that is to say without undesired interruption, in order to thereby achieve the desired mixing result.